Optical logic gates have been the subject of research for several decades due to the possibility of achieving higher operating speeds than logic based on electronics. The advantages of digital signal processing in the optical domain include higher signal bandwidth, lower signal cross-talk, and greater protection against electronic eavesdropping. All-optical signal processing also eliminates the need to convert signals from the optical domain into the electronic domain for processing and then to re-convert the processed signals from the electronic domain back into the optical domain. All-optical signal processing is advantageous to reduce the cost, electrical power requirement, size and weight compared to optical-to-electronic converters, electronic signal processing circuitry, and electronic-to-optical converters which are currently being used.
The present invention addresses the need for optical logic gates by providing an optical exclusive or (also termed XOR) gate which can be formed as a photonic integrated circuit (PIC) using two electroabsorption modulator (EAM) photodiode (PD) pairs, with each EAM/PD pair being electrically connected together in series. This configuration according to the present invention provides advantages in terms of optical isolation of input and output signals, an ability to be monolithically integrated, and an ability to operate using direct-current electrical power sources with a relatively low power consumption and a relatively compact size. The present invention is also advantageous in providing for optical signal gain and regeneration thereby permitting a fan out capability which can allow multiple optical XOR gates to be interconnected together or to be interconnected to the optical logic gates disclosed in U.S. patent application Ser. Nos. 12/182,683 and 12/270,221 and to an optical data latch disclosed in U.S. Pat. No. 7,787,719 to provide a high level of logic functionality for optical signal processing or optical computing applications.
These and other advantages of the present invention will become evident to those skilled in the art.